An etching gas for etching an oxide film formed on a substrate, includes a main gas composed of an unsaturated fluorocarbon-based gas; and an additive gas composed of a straight-chain saturated fluorocarbon-based gas expressed by CXF(2X+2) (x represents a natural number of 5 or larger). The additive gas is C5F12 gas, C6F14 gas or C7F16 gas. Another etching gas includes a main gas composed of an unsaturated fluorocarbon-based gas; and an additive gas composed of a cyclic saturated fluorocarbon-based gas expressed by CXF2X (X represents a natural number of 5 or larger). In this case, the additive gas is C5F10 gas or C6F12 gas.
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1. A method for etching an oxide film formed on a substrate, comprising the steps of:
introducing an etching gas including a main gas composed of an unsaturated fluorocarbon-based gas having at least five carbon atoms and an additive gas composed of a straight-chain saturated fluorocarbon-based gas consisting of C5F12 or C6F14; and
etching the oxide film on the substrate in a plasma atmosphere within the processing chamber.
5. A method for evaluating an etching gas including a main gas composed of an unsaturated fluorocarbon-based gas and an additive gas composed of a cyclic saturated fluorocarbon-based gas expressed by CXF2X, wherein x represents a natural number of 5 or larger, comprising:
performing a simulation of the etching gas prior to an actual etching process by decomposing in a mass spectrometer the etching gas into a multiplicity of fluorocarbon ions by supplying an electronic energy and detecting types of the fluorocarbon ions generated from the etching gas in an etching process and a composition ratio of each of the fluorocarbon ions;
calculating a value expressed by P×NF/(M)0.5 indicating a level of impact amount of fluorine atoms of each of the fluorocarbon ions per unit time against the substrate in the etching process based on the mass M, the number of fluorine atoms NF and the composition ratio p of each of the fluorocarbon ions detected;
adding up all of those calculated values, to thereby obtain a total added value; and
evaluating prior to said actual etching process the etching rate of the etching process based on the total added value.
9. A method for evaluating an etching gas including a main gas composed of an unsaturated fluorocarbon-based gas and an additive gas composed of a fluorocarbon-based gas expressed by CXF(2X+2) or CXF2X, wherein x represents a natural number of 5 or larger, comprising:
performing a simulation of the etching gas prior to an actual etching process by decomposing in a mass spectrometer the etching gas into a multiplicity of fluorocarbon ions by supplying an electronic energy to the etching gas and detecting types of the fluorocarbon ions generated from the etching gas in an etching process and a composition ratio of each of the fluorocarbon ions;
calculating a value expressed by P×NF/(M)0.5 indicating a level of impact amount of fluorine atoms of each of the fluorocarbon ions per unit time against the substrate in the etching process based on the mass M, the number of fluorine atoms NF and the composition ratio p of each of the fluorocarbon ions detected;
adding up all of those calculated values, to thereby obtain a total added value; and
evaluating prior to said actual etching process the etching rate of the etching process based on the total added value.
2. The method of
3. A method for evaluating an etching gas described in
performing a simulation of the etching gas prior to an actual etching process by decomposing in a mass spectrometer the etching gas into a multiplicity of fluorocarbon ions by supplying an electronic energy and detecting types of the fluorocarbon ions generated from the etching gas in an etching process and a composition ratio of each of the fluorocarbon ions;
calculating a value expressed by P×NF/(M)0.5 indicating a level of impact amount of fluorine atoms of each of the fluorocarbon ions per unit time against the substrate in the etching process based on the mass M, the number of fluorine atoms NF and the composition ratio p of each of the fluorocarbon ions detected;
adding up all of those calculated values, to thereby obtain a total added value; and
evaluating prior to said actual etching process the etching rate of the etching process based on the total added value.
4. The method of
calculating a value expressed by P×NC/(M)0.5 indicating a level of impact amount of carbon atoms of each of the fluorocarbon ions per unit time against the substrate in the etching process based on the mass M, the number of carbon atoms NC and the composition ratio p of each of the fluorocarbon ions detected;
adding up all of those calculated values, to thereby obtain a total added value; and
evaluating the etching selectivity of the etching process using the etching gas based on the total added value.
6. The method of
calculating a value expressed by P×NC/(M)0.5 indicating a level of impact amount of carbon atoms of each of the fluorocarbon ions per unit time against the substrate in the etching process based on the mass M, the number of carbon atoms NC and the composition ratio p of each of the fluorocarbon ions detected;
adding up all of those calculated values, to thereby obtain a total added value; and
evaluating the etching selectivity of the etching process using the etching gas based on the total added value.
10. The method of
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The present invention relates to an etching gas for etching an oxide film on a substrate, an etching method using the etching gas, and an evaluation method for the etching gas.
In a manufacturing process of a semiconductor device using a photolithography technique, etching is used to be performed on a silicon oxide film (SiO2 film) used as, e.g., an insulation film and the like. For example, in a parallel plate type processing apparatus, the etching on the silicon oxide film is performed by ionizing an etching gas in a plasma atmosphere to allow the ionized etching gas to chemically react with the silicon oxide film.
In general, a fluorocarbon-based gas whose chemical formula is expressed by CxFy (x, y represent natural numbers) has been used as an etching gas for etching the silicon oxide film. Conventionally, a low-order saturated fluorocarbon-based gas such as CF4 and C4F8 having a small number of carbon atoms is used to be employed. Recently, however, an unsaturated fluorocarbon-based gas such as C4F6 begins to be used as the etching gas (see, for example, Japanese Patent Laid-open Application No. H6-275568). Since the unsaturated etching gas is difficult to be decomposed and easy to be polymerized in comparison with the conventional one, it would be deposited on a mask surface of the silicon oxide film as a protection film to thereby provide a high etching selectivity.
In case of using the unsaturated etching gas such as C4F6, however, the ratio of fluorine atoms to carbon atoms is decreased and at the same time, the absolute amount of the fluorine atoms gets reduced compared with the case of using the saturated gas such as CF4, resulting in a reduction of an etching rate. Since single sheet type etching apparatuses have been most commonly employed in recent days, the reduction of the etching rate would result in a significant decrease in productivity of semiconductor devices.
It is, therefore, an object of the present invention to provide an etching gas capable of etching an oxide film such as a silicon oxide film at a high etching rate while maintaining a high etching selectivity; an etching method using the etching gas; and an evaluation method for the etching gas.
In accordance with one aspect of the present invention, there is provided an etching gas for etching an oxide film formed on a substrate, including: a main gas composed of an unsaturated fluorocarbon-based gas; and an additive gas composed of a straight-chain saturated fluorocarbon-based gas expressed by CxF(2x+2) (x represents a natural number of 5 or larger).
The inventors have found that, by adding to the main gas composed of an unsaturated fluorocarbon-based gas the additive gas composed of a straight-chain saturated fluorocarbon-based gas expressed by CxF(2x+2) (x represents an integer of 5 or larger), it is possible to increase an etching rate while maintaining a high etching selectivity. The additive gas may be C5F12 gas, C6F14 gas or C7F16 gas.
In accordance with another aspect of the present invention, there is provided an etching gas for etching an oxide film formed on a substrate, including: a main gas composed of an unsaturated fluorocarbon-based gas; and an additive gas composed of a cyclic saturated fluorocarbon-based gas expressed by CxF2x (x represents a natural number of 5 or larger).
The inventors have found that, by adding to the main gas composed of an unsaturated fluorocarbon-based gas the additive gas composed of a cyclic saturated fluorocarbon-based gas expressed by CxF2x (x represents a natural number of 5 or larger), it is possible to increase an etching rate while maintaining a high etching selectivity. In addition, in this case, the etching selectivity can be further increased compared with that in the case of adding the straight-chain saturated fluorocarbon-based gas. Furthermore, the additive gas may be C5F10 gas or C6F12 gas.
The main gas may be C5F8 gas or C4F6 gas. The C5F8 gas includes cyclic c-C5F8 gas, straight-chain 1,3-C5F8 gas and 2-C5F8 gas. Further, the C4F6 gas includes cyclic c-C4F6 gas, straight-chain 1,3-C4F6 gas and 2-C4F6 gas.
The main gas may be a cyclic unsaturated fluorocarbon-based gas, such as either C6F6 gas or C7F8 gas.
In accordance with still another aspect of the present invention, there is provided a method for etching an oxide film formed on a substrate, including the steps of: introducing an etching gas including a main gas composed of an unsaturated fluorocarbon-based gas and an additive gas composed of a straight-chain saturated fluorocarbon-based gas expressed by CxF(2x+2) (x represents a natural number of 5 or larger) into a processing chamber; and etching the oxide film on the substrate in a plasma atmosphere within the processing chamber.
In this case, it is possible to increase an etching rate while maintaining a high etching selectivity. Further, the additive gas may be C5F12 gas, C6F14 gas or C7F16 gas.
In accordance with still another aspect of the present invention, there is provided a method for etching an oxide film formed on a substrate, including the steps of: introducing an etching gas including a main gas composed of an unsaturated fluorocarbon-based gas and an additive gas composed of a cyclic saturated fluorocarbon-based gas expressed by CxF2x (x represents a natural number of 5 or larger) into a processing chamber; and etching the oxide film on the substrate in a plasma atmosphere within the processing chamber.
With such method, it is possible to increase an etching rate while maintaining a high etching selectivity. Further, the additive gas may be C5F10 gas or C6F12 gas.
The main gas may be either C5F8 gas or C4F6 gas. Further, the main gas may be a cyclic unsaturated fluorocarbon-based gas such as either C6F6 gas or C7F8 gas.
In accordance with still another aspect of the present invention, there is provided a method for evaluating any one of the etching gases described above, including the steps of: decomposing an etching gas into a multiplicity of fluorocarbon ions by applying an electronic energy and detecting types of the fluorocarbon ions generated from the etching gas in an etching process and a composition ratio of each of the fluorocarbon ions, by using a mass spectrometer; calculating a value expressed by P×NF/(M)0.5 indicating a level of impact amount of fluorine atoms of each of the fluorocarbon ions per unit time against the substrate in the etching process based on the mass M, the number of fluorine atoms NF and the composition ratio P of each of the fluorocarbon ions detected; adding up all of those calculated values, to thereby obtain a total added value; and evaluating the etching rate of the etching process by using the etching gas based on the total added value. Further, the term “composition ratio” means an occupancy ratio of each fluorocarbon ion with respect to the total number of ions of the generated fluorocarbon ions.
In accordance with the evaluation method of the present invention, the evaluation of an etching gas can be carried out without performing an actual etching process. As a result, time and cost required to develop an etching gas can be reduced, thereby efficiently performing the development of the etching gas.
The above evaluation method may further include the steps of: calculating a value expressed by P×NC/(M)0.5 indicating a level of impact amount of carbon atoms of each of the fluorocarbon ions per unit time against the substrate in the etching process based on the mass M, the number of carbon atoms NC and the composition ratio P of each of the fluorocarbon ions detected; adding up all of those calculated values, to thereby obtain a total added value; and evaluating the etching selectivity of the etching process by using the etching gas based on the total added value.
In accordance with the present invention, in etching an oxide film, it is possible to increase an etching rate while maintaining a high etching selectivity, thereby resulting in, e.g., an increased productivity of semiconductor devices.
The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:
Hereinafter, preferred embodiments of the present invention will be described in detail.
As shown in
An upper electrode 10 of, e.g., a disc shape is disposed at a ceiling portion of a processing chamber 2, wherein the ceiling portion is configured to face a mounting surface of the lower electrode 3. An annular insulator 11 is interposed between the upper electrode 10 and the processing vessel 2 such that the upper electrode 10 and the processing vessel 2 are electrically isolated from each other. A second high frequency power supply 13 for generating plasma is connected to the upper electrode 10 via a matching unit 12.
Moreover, a high frequency power of a frequency equal to or higher than, for example, 30 MHz is applied to the upper electrode 10 from the second high frequency power supply 13. On the other hand, a high frequency power of a frequency lower than that of the high frequency power from the second high frequency power supply 13, for example, a high frequency power of a frequency ranging from, e.g., about 1 to 30 MHz is applied to the lower electrode 3 from the first high frequency power supply 7.
The upper electrode 10 is provided at its lower surface with a number of gas discharge openings 10a through which an etching gas is discharged into the processing vessel 2. The gas discharge openings 10a communicate with a gas supply line 20 connected to an upper surface of the upper electrode 10. The gas supply line 20 is connected in turn to, for example, three gas supply systems, i.e., to a first to a third gas supply system 21 to 23. The three gas supply systems 21 to 23 are coupled to gas supply sources 30 to 32 via opening/closing valves 24 to 26 and mass flow controllers 27 to 29, respectively. In the preferred embodiment, an unsaturated fluorocarbon-based gas, for example, c-C5F8 gas can be supplied from the gas supply system 21 as a main gas. Further, a straight-chain saturated fluorocarbon-based gas expressed by CxF(2x+2) (x represents a natural number), for example, C5F12 gas can be supplied from the second gas supply system 22 as an additive gas. Moreover, for example, He gas can be supplied from the third gas supply system 23 as a rare gas species. The chemical constitutional formulas of the c-C5F8 gas and the C5F12 gas are illustrated in
A gas exhaust line 40 connected with a gas exhausting mechanism (not shown) is coupled to a lower portion of the processing vessel 2. By vacuum evacuating the processing vessel 2 via the gas exhaust line 40, the internal pressure of the processing vessel 2 can be maintained at a preset level.
An etching method employed by the plasma etching apparatus 1 with the above configuration will now be described for the case of etching, for example, a silicon oxide film formed on a wafer W. First, the wafer W is loaded into the processing vessel 2 to be mounted on the lower electrode 3 and is maintained thereon by being attracted by the electrostatic chuck 5. Then, the processing vessel 2 is evacuated via the gas exhaust line 40, and a predetermined etching gas is supplied into the processing vessel 2 through the gas discharge openings 10a. The processing vessel 2 is maintained at a preset vacuum level, for instance, about 4 Pa (30 mTorr).
The etching gas discharged through the gas discharge openings 10a includes the c-C5F8 gas, the C5F12 gas and the He gas supplied from the gas supply systems 21 to 23, respectively. The flow rate ratio of the c-C5F8 gas and the C5F12 gas is set to be 1 to 0.5˜1.
If the internal pressure of the processing vessel 2 reaches the preset vacuum level, a high frequency power of, e.g., 13.56 MHz and 2 kW is applied to the lower electrode 3 from the first high frequency power supply 7, and a high frequency power of, e.g., 60 MHz and 2 kW is applied to the upper electrode 10 from the second high frequency power supply 13. As a result, plasma is generated within the processing vessel 2, the etching gas is ionized and then the etching is performed on the silicon oxide film on the wafer W. After a lapse of a predetermined time period, the application of the high frequency powers and the supply of the etching gas are stopped, and the wafer W is unloaded from the processing vessel 2, thus completing the etching process.
When performing an etching by adding the high-order straight-chain saturated C5F12 gas to the unsaturated c-C5F8 gas serving as a main gas as in the preferred embodiment of the present invention, a simulation result conducted by the inventors revealed that the etching rate was increased by 126% in comparison with a case of using no additive gas, as shown in
Accordingly, by using the c-C5F8 gas as a main gas and adding the C5F12 gas or the C6F14 gas thereto, etching rate can be improved greatly, while maintaining the high etching selectivity.
Though the above preferred embodiment has been described for the cases of using the C5F12 gas and the C6F14 gas as an additive gas, any straight-chain saturated fluorocarbon-based gas expressed by CxF(2+2) (x represents a natural number of 7 or larger), for example, C7F16 gas, may be employed. Since these fluorocarbon-based gases have same characteristics as those of the C5F12 gas or the C6F14 gas, a high etching rate can be obtained similarly as in the above preferred embodiment when they are used as an additive gas.
Moreover, in the above-described preferred embodiment, same effects can be achieved by using 1,3-C5F8 gas or 2-C5F8 gas instead of the c-C5F8 gas as the main gas. Further, it is also possible to achieve the same effects by using any unsaturated fluorocarbon-based gas other than the C5F8 gas, for example, C4F6 gas. Here, the C4F6 gas may be a cyclic c-C4F6 gas, straight-chain 1,3-C4F6 gas or straight-chain 2-C4F6 gas.
Though the He gas is supplied into the processing vessel 2 from the third gas supply system 23 during the etching process, another rare gas species such as Ne gas, Ar gas or Xe gas can be supplied instead. Further, oxygen gas or a nonreactive gas may be supplied in lieu of the rare gas species.
Furthermore, though as the additive gas, a straight-chain saturated fluorocarbon-based gas expressed by CxF(2x+2) (x represents a natural number of 5 or larger) was used in the above-described preferred embodiment, a cyclic saturated fluorocarbon-based gas expressed by CxF(2x) (x represents a natural number of 5 or larger) could be used instead. According to a simulation result provided in
Though the unsaturated C5F8 gas is used as the main gas in the preferred embodiment, a higher-order cyclic unsaturated carbon based gas having at least 6 carbon atoms may be employed instead. The simulation result in
In the above-described preferred embodiment, however, the etching rate and the etching selectivity of each etching gas are determined through simulations. Conventionally, in order to evaluate a new etching gas, an etching process has to be actually performed in an etching apparatus by using the new etching gas, and the evaluation of the etching gas is carried out by accumulating thus obtained data. However, this conventional evaluation method is time-consuming because an actual processing has to be performed whenever the evaluation of an etching gas is necessary. Furthermore, in case the evaluation result of the etching gas is poor, the experiment would turn out to be a waste of time. Still further, in the conventional method, one has to have an experimental equipment such as the etching apparatus to develop a new etching gas. Here, as a solution to these problems of the conventional evaluation method, a new method employing a simulation for evaluating an etching gas will be proposed. Hereinafter, the etching gas evaluation method will be described.
In a mass spectrometer 100 illustrated in
For example, when the etching gas to be evaluated is C2F6 gas, a mass spectrum is obtained as shown in
Thereafter, data of the fluorocarbon ions detected by the mass spectrometer 100 is inputted to a computer 101, as shown in
An impact amount HFS of the fluorine atoms of each fluorocarbon ion can be expressed by a multiplication of the number NF of fluorine atoms, the composition ratio PX and a speed V of each fluorocarbon ion, i.e., HFS=PX×NF×V. The speed V of each fluorocarbon ion can be expressed by V=(2e/M)(0.5) from the equation of kinetic energy (e=½×MV2). Accordingly, the impact amount HFS can be expressed by HFS=PX×NF×V=PX×NF×(2e/M)(0.5). If the incident ion energy is constant, the speed V of each fluorocarbon ion is in proportion to 1/M(0.5), so that a relationship of HFS ∝ PX×NF/(M)(0.5) is obtained. Consequently, a value HF representing a level of the impact amount HFS can be expressed by HF=PX×NF/(M)(0.5) ∝ HFS.
For example, as for C2F6 gas as shown in
Then, the values HF of the fluorocarbon ions are all added up (S3 in
Moreover, based on the mass M, the composition ratio PX and the number NC of carbon atoms of each fluorocarbon ion detected by the mass spectrometer 100, the computer 101 calculates a value HC representing a level of impact amount of carbon atoms of each fluorocarbon ion against the wafer W per unit time (S5 in
For example, in case of the C2F6 gas as shown in
Then, the values HC of the fluorocarbon ions are all added up (S6 in
Moreover, the above-described etching gas evaluation method may be applied for the evaluation of an etching gas other than the fluorocarbon-based gas. That is, the etching gas evaluation method may include the steps of decomposing an etching gas into a number of ions by applying a preset electronic energy and detecting the types of ions generated from the etching gas during an etching process and their composition ratios, by using a mass spectrometer; calculating a value expressed by P×NI/(M)0.5 indicating a level of impact amount of an element, which constitutes each ion and affects the etching rate, against a substrate per unit time during the etching process based on the detected mass M and composition ratio P of each ion and the atom number NI of the element; adding up all of those calculated values to thereby obtain a total added value; and evaluating the etching rate of the etching process by using the etching gas based on the total added value.
Further, the etching gas evaluation method may further include the steps of calculating a value expressed by P×NII/(M)0.5 indicating a level of impact amount of another element, which constitutes each ion and affects the etching rate, against the substrate per unit time during the etching process based on the detected mass M and composition ratio P of each ion and the atom number NII of the another element; adding up all of those calculated values, to thereby obtain a total added value; and evaluating the etching rate of the etching process by using the etching gas based on the total added value. The etching gas evaluation method can be applied to the evaluation of an etching gas formed of an organic material, for example, NH3 gas.
Although there have been described the preferred embodiments of the present invention, the present invention is not limited thereto. For example, though the case of etching a semiconductor wafer has been exemplified in the preferred embodiment, the present invention may be applied to the etching of other types of substrates including, for example, a substrate for a flat panel display (FPD), a glass substrate for a photomask, and so forth.
In accordance with the present invention, it is possible to improve an etching rate while maintaining a high etching selectivity in case of etching an oxide film.
While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.
Honda, Masanobu, Nagaseki, Kazuya, Kitamura, Akinori
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